


Instruction

by the1eyedtree



Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Angst, Fire Emblem: Three Houses Blue Lions Route, Fluff and Smut, M/M, Male My Unit | Byleth, Mutual Pining, Not really any spoilers aside from the state everyone's in post timeskip, Pining, Porn With Plot, Porn with Feelings, Post-Timeskip | War Phase (Fire Emblem: Three Houses), Sex, Smut, just dudes not communicating their feelings lol
Language: English
Status: In-Progress
Published: 2019-09-10
Updated: 2019-09-11
Packaged: 2020-10-13 18:17:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,351
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20586908
Author URL: https://archiveofourown.org/users/the1eyedtree/pseuds/the1eyedtree
Summary: “He could honestly just use a good fuck.”Everyone’s eyes snapped to Sylvain who had spoken. Byleth could see Ingrid bristle as if she were about to jump across the table and strangle her comrade. Everyone else remained still, expecting some sort of punchline or ‘just kidding,’ but Sylvain had a serious look on his face.“I’m not joking, guys.”The Blue Lions are desperate to do anything to make their prince feel better -- desperate enough to actually listen to Sylvain. And thus Sylvain must teach the professor how to have intercourse, but in that falls for the man himself. But saving the Kingdom is more important than his heart, right?





	1. Chapter 1

“Professor, what are we supposed to do about Dimitri?” Byleth looked up, pulled from his inner musings back to reality at Annette’s question. The students had wanted to meet with him to discuss strategies to bring their prince back from the edge, but he himself had no idea where to even begin. At his silence, Mercedes spoke up.

“It seems that nothing we’ve done so far has helped,” her voice was void of its normal optimism.

“Drinking tea does not save people,” Felix cut in. Byleth noticed Mercedes’s shoulders drop just a fraction in defeat, but her face remained calm.

“What could even possibly help someone in that state?” Ingrid’s brow was furrowed in frustrated concern.

“Some people turn to alcohol, but that normally hurts more than it heals,” Ashe mused. Byleth crossed his arms in contemplation. The room was quiet for many moments.

“He could honestly just use a good fuck.”

Everyone’s eyes snapped to Sylvain who had spoken. Byleth could see Ingrid bristle as if she were about to jump across the table and strangle her comrade. Everyone else remained still, expecting some sort of punchline or ‘just kidding,’ but Sylvain had a serious look on his face.

“I’m not joking, guys.”

The other students all began speaking at once, chastising him. Byleth held up a hand to silence them, then looked to Sylvain who desperately looked as if he wanted to continue speaking. With a nod from the professor, Sylvain spoke again.

“There’s actually science behind this kinda thing. The dose of chemicals that flood your nerve system during an orgasm can help in situations like his highness’s…” Sylvain seemed to hesitate to continue with so many people staring daggers at him.

“That is actually quite correct.” All eyes, including Sylvain’s, snapped to Mercedes as she spoke. “There is evidence that the chemicals that are released when having intercourse have similar effects on the body as healing magic.” The room was filled with shocked silence.

“In that regard, this could work,” Byleth said. He locked eyes with Sylvain, whose cheeks were just pink enough for him to notice the blush.

“Professor, is that really a good idea?” Ingrid asked.

“We cannot seem to think of other effective ideas, and the situation needs to change soon.” Byleth’s voice rang with authority.

“A solution fit for a beast,” Felix stated.

“But who would, um, participate in this plan?” Sylvain asked. Everyone looked around at each other.

“I will,” Byleth said, standing up. No one could exactly argue with him on this, though he could see that most everyone in the room was increasingly uncomfortable with this conversation. “Let us adjourn this meeting for now.”

The room cleared out pretty quickly, yet Sylvain remained behind. He approached Byleth, his care-free posture not quite making it to his face.

“Um, I, uh, thanks for actually considering my idea, Teach.” He was about to leave when Byleth put a hand on his shoulder.

“I may need help with this plan,” Byleth admitted, pulling his hand away slowly. Sylvain furrowed his brow, gave him a full glance over, and then cocked a coy smirk.

“You’re still a virgin?”

Byleth nodded, though he felt no shame. _Should he feel ashamed for not having had sex before?_ Sylvain’s blush deepened, but his smirk remained.

“You shouldn’t go into this without the proper skills, or you might actually get killed.”

…

Sylvain shook his head as he walked down the corridor later that night. He couldn’t believe the situation was real and that he was a part of it. He was supposed to be meeting with the professor in one of the vacant dorms for a….lesson.

_I can’t believe this idea even got approved._

Sylvain ran a hand through his red hair to settle himself. A blush burning lightly on his cheeks, he shook his head – he was about to genuinely teach _his teacher_ how to have sex. It’s not like he didn’t know the ins and outs (_ha_) of the act, but every step that brought him closer to the meeting place made the situation all the more real and that made him incredibly anxious.

_Surely the professor knows more about sex than he was letting on. Right? RIGHT?_

But now, Sylvain found himself at the door of where he was to meet the professor. He took a deep breath. He could do this. He just had to remain calm.

He knocked on the door with a few short raps. He heard a muffled “come in” and opened the door. He quickly surveyed the room and noticed a bed that was larger than his own (though it had clearly not been used in years), a table with a single lit candle upon it, and his professor, who was just standing in the middle of the room. Amber eyes met pale green, as both men sized the situation up.

“You can come all the way in – you’re letting in a draft,” the professor pointed out.

“Oh, right!” Sylvain quickly closed the door behind himself and walked toward the profes-Byleth.

_It’d be better to just use his name instead of his title to make this less weird._

Byleth looked at the red head with the same placid calmness as if they were about to go fishing together (_and not bang each other_.) Sylvain took in a deep breath.

“Just to make sure, you _are_ okay with this, right?”

Byleth nodded.

“But you’ve never had sex before?”

Another nod.

“What do you know about sex?”

Byleth placed his hand on his own chin in thought.

“It happens on a bed?”

_Oh, Goddess how is this even real?_

“Well, some people do it on beds, yeah, but location really doesn’t actually matter to the process.” Sylvain sighed, trying to put his thoughts into _appropriate_ words. “In this case… someone’s dick goes up someone’s butt.”

There was only silence.

Then Byleth raised his hand.

“Yeah?”

“Up whose butt?”

Sylvain honestly could not keep the chuckle that bubbled up his chest from escaping.

“Uh, well, ha, we’ll figure that out once we’re there. First, you need to know about the most important part of sex: foreplay.”

Byleth nodded intently as if this really were just an ordinary lesson. That somehow gave Sylvain the confidence to keep going.

“Foreplay is of course a great way to get into ‘the mood,’ but it’s also good for making sure the other person is into doing it too – course that doesn’t really apply to the situation you’ll be in because you probably won’t have a chance to let his Highness decide.” Byleth listened to everything the other said, keeping a running list of important things to remember in his head.

“Okay, well now this next part is better shown than told, but um…just trust me, alright?” Sylvain’s eyes held a level of sincerity that Byleth had only ever seen on the battlefield.

“I trust you.”

“Okay, now pay attention to everything I do because it’s what you’ll need to do.” Another nod from Byleth, and Sylvain closed the distance between them. He cupped the other’s cheeks and pulled him in for a kiss. Byleth remained still, listening with his body to Sylvain’s teachings. The cavalier urged the ex-mercenary’s mouth open and began to swirl his tongue. Byleth couldn’t help but lean into him, captivated by this experience. Sylvain pulled away momentarily to catch his breath and give more instruction.

“Now is when you want to start using your hands,” his left hand was placed on Byleth’s waist, while the other hand slid from his cheek to his chest. Sylvain then pulled away completely. “You try.”

Byleth nodded and closed the gap between them. He pressed his lips against the other’s and counted out the same number of seconds that had passed before between the start of the kiss and the tongue part. He attempted to be as gentle as Sylvain had and worked his mouth open and slid his tongue inside. He also slid his hands into the same position that the other had shown him just before. Sylvain let out a chuckle that vibrated surprisingly pleasingly between them.

“You don’t have to 100% copy everything I do – just take it all as inspiration,” Sylvain said as he pulled away a bit. The two men looked at each other, and Byleth fully stepped back.

“Perhaps it would be better to show me the process as a whole, and I will ask questions should I need to.” The professor’s voice was cool and even – which Sylvain was a bit jealous of because he was having a hard time keeping his heart rate in check.

“Sure, yeah that will probably work better.” He took a deep breath. “Okay, ready?”

At Byleth’s nod, Sylvain quickly pulled their bodies together and pressed into another kiss. His hands deftly danced across Byleth’s body, before he spun them both around and pushed toward the bed. Once they fell upon it, Sylvain pulled away again.

“Now is when we need to decide if you’ll be a top or bottom.”

“A what?”

“To answer your question from before, the top puts his dick in the bottom’s butt.”

“Oh,” Byleth looked off into the distance for a moment as he contemplated.

“I think it’s safe to assume that Dimitri is a top, but for the purpose of ‘helping’ him I think having him in a more submissive position would be bett-,”

“I want to top.” There was a gleam in Byleth’s eyes that Sylvain couldn’t quite read, but it seemed to promise an interesting time.

“Okay then, I’ll teach you how to top.” Sylvain hoped his voice sounded at least half as calm as Byleth’s. “The first thing to remember as the top, is to properly prepare your bottom.”

Sylvain reached around to a pouch that was at his side. He pulled out a small bottle.

“This is a special oil that mitigates friction, you’ll need it in a bit so I’m just gonna set it over here.” The red head put the bottle on the other side of the bed, and then began to take of his shirt. He’d be lying if being watched so intently by Byleth wasn’t doing a number to his body. Once he was free of most of his clothes, he paused.

“Should I also remove my clothing?” Byleth asked.

“Um, yeah, it levels the playing field if all parties are disrobed.” Sylvain wanted to slap himself at how his voice was beginning to portray his growing desire. Byleth simply nodded and quickly began to work himself out of his armor. Sylvain couldn’t help but watch as more and more pale skin was revealed.

“Pants too?” Byleth’s voice snapped Sylvain back to reality. He wasn’t sure there was enough time in the universe to prepare himself to completely reveal himself to Byleth. But it would be _really_ awkward if he stopped now.

“Just me for now – after the preparation is complete, you can remove yours.” Sylvain sucked in a deep breath and pulled his pants and underwear off in one surprisingly graceful motion and tossed them to the ground. He was already hardening, but he couldn’t help but squirm a bit under Byleth’s gaze. The red head had never been looked at like this. He couldn’t tell if he was more turned on or terrified. But he needed to keep going.

“Now you’ll need to prepare my…ass by using that oil and your hands…” Sylvain shook his head in an attempt to clear it. “Actually, you know what,” a sudden gleam appeared in his eyes as he got an idea, “this is another instance that is better shown. Go ahead and take off your pants.” Byleth complied, and suddenly all of each of them was fully revealed. Sylvain swallowed hard – no one that he had ever laid with had _anything_ on Byleth. Everything his eyes saw was magnificent. He reached for the bottle and poured some of its contents over his fingers. He held up his lubricated hand. “Remember: **always** start with one finger.” Byleth had a bit more of a curious gleam in his eye now. “I’m going to show you how to properly prepare on your body first, and then you’ll…” Sylvain had to take another deep breath. “You’ll practice on me.”

Sylvain gently repositioned Byleth so he could easily reach his ass.

“Ready?”

Byleth nodded, yet again.

Sylvain tried to will some of the blood in his body to remain in his head and not rush to his dick. He slowly ran a finger up the inside of Byleth’s left thigh, traced around his entrance, and pressed in. Byleth’s eyes fluttered closed, he wasn’t entirely sure how to comprehend the sensation. Sylvain’s other hand appeared on his stomach and urged him back into a relaxed position. They sat there for a few moments, both to let Byleth adjust and because Sylvain was terrified. When Byleth opened his eyes again, his expression was as cool as ever, and a spark of inspiration erupted in Sylvain – he was going to destroy that coolness and make Byleth come undone if it was the last thing he ever did. And so, he began working his finger into Byleth. The latter’s eyes snapped shut when Sylvain curled his finger slightly. The cool expression dropped for a glorious moment. Sylvain knew he was good with his hands, but this confirmation sent a shiver down his spine.

But there was so much more that Byleth needed to know.

Sylvain gently pulled his hand back and relished in the disappointed look that flashed across Byleth’s face. The latter looked up at him in question.

“Now, it’s your turn…to uh, prep me.” Goddess, he could hear his arousal in his own voice. Byleth let out a slow breath, and then gracefully pulled Sylvain over and rolled on top of him. Whatever blood was left in his brain rushed downwards as Sylvain watched Byleth pour the oil over his hand. They locked eyes.

“Ready?”

It was Sylvain’s turn to nod – though he wasn’t even sure if he could speak anymore. Once again Byleth did just as Sylvain, and by the goddess it felt good.

“Now you can add another finger…” It took all he had not to let out a moan as another finger slid in as he spoke. “Mm-hm like that..the g-goal is to make sure y-you can fit your..ah” Byleth had found the bundle of nerves that would be Sylvain’s undoing. “You know, that’s p-probably enough – next phase.”

Sylvain’s cheeks were burning hot, and his thoughts were beginning to blend together in arousal induced chaos. He took a deep breath and tried to look anywhere but Byleth to clear his head.

“Should I use the oil on my penis?”

Sylvain almost burst – the odd mix of naivety and masterful skills was arousing him so much more than anything that he could think of ever had. He shouldn’t be this attracted to this.

_I shouldn’t be this attracted to him._

“Mm-yeah, yes, that would be best,” he answered. His eyes followed the oil as it spilled from the bottle and onto Byleth, and without thinking about it, Sylvain reached for the other’s penis and began working it with his hand. Byleth hummed in assent and surprisingly relaxed into Sylvain’s hold.

_I shouldn’t feel things for him._

When Byleth as hard and firm, and- _Is his breathing uneven?_ Sylvain pulled his hand back and repositioned himself into a more, well, fuckable position.

“When you’re both ready, you can put it in, and oh – ‘nother important thing to remember: let your bottom** adjust**.”

Byleth nodded again, but his eyes held a more feral look, and Sylvain felt himself twitch in anticipation.

“You can go on and do it,” Sylvain urged. And with that, Byleth gently inserted himself into him.

_Oh Goddess…_

He must have looked in pain because Byleth had leaned in closer and cupped his cheek with his unlubricated hand.

“Is this alright?” he asked, and Sylvain just managed a nod. He raised a hand and placed it over Byleth’s. And _damn him_ he was smiling at Sylvain.

_He likes this, too?_

Byleth braced his other arm on the bed and began to slowly move in and out of Sylvain. They went on like this for a while, and Sylvain managed to keep a level head, _barely_, to lead them through it. Suddenly, Byleth kissed him, and Sylvain nearly came. The red head held their faces together with one hand, and with the other he reached for himself. Byleth pulled away just a fraction.

“I think..mm about to b-burst,” Byleth stuttered out, nearly making Sylvain lose it, _again_.

“Ngn, pull out, I’ll help.”

Byleth followed his instruction and Sylvain took them both in hand shortly after Byleth spilled onto him. Sylvain couldn’t look away from the masterpiece of Byleth coming undone. This sent him spilling over as well.

Both men were panting, trying to come back to reality.

“I have made a mess on you.” Byleth sounded so apologetic. Sylvain chuckled.

“It’s fine,” he said, using the old bedding to wipe himself off.

_That was so nice._

_Best I’ve had._

_Oh shit._

Sylvain rolled out from under Byleth and off the bed. He grabbed his clothes and pulled on his pants. Without looking back he spoke,

“And that’s that, any questions?” There was a moment of contemplative silence.

“Not at the moment.”

“Good, I’ll be going then. You can keep the oil – you’re gonna need it.” Sylvain knew he sounded curt, but he needed to get out of there _fast_. Without waiting for a response, Sylvain all but high-tailed it out of the room and bee lined to his room.

_I think I love my professor_.


	2. Chapter 2

Sylvain couldn’t help the knot in his stomach as he approached the door of the Cardinal’s Room. He was summoned here to be a part of a strategy meeting regarding ‘subduing the beast’ as Felix refers to it. Taking a deep breath, he pushed the doors open and took note of all who were present. Felix had his arms crossed and was leaning as far away from the table as possible in his seat; Ingrid was sitting with all the proper posture and prowess as a noble should and looked like she was ready to take notes, _goddess_,_ what kind of plan were they going to have to carry it out?_

And then there was Byleth standing at the far head of the table. Sylvain did his best to ignore the way his stomach flipped at the way the light from the windows cut across his _<strike>beautiful</strike>_ face. Avoiding any more eye contact, Sylvain flopped down into his usual seat and tried (and almost succeeding) to maintain his normal leisurely posture.

“Now that everyone is here, we shall begin.” Byleth’s voice was smooth as ever _damn him_.

“Wait, it’s just us?” Ingrid leaned forward, gesturing to herself, Sylvain, and Felix. Byleth nodded.

“It’s better that we keep a mission such as this under wraps,” he spoke with clarity.

“Right, a mission ‘such as this’.” Ingrid tried to hide her blush by leaning her face on her hand.

“Why am I even here?” Felix asked as he does in almost every situation.

“The plan is to subdue Dimitri in one of the unused dormitories, but as we are all aware the situation could turn dangerous at any given point,” Byleth explained. Sylvain was doing all he could to not look at the man, or the way his armored hands moved gracefully, or the way his hair caught on the neck of his armor….No, Sylvain wasn’t noticing these things at all. “So, the plan is to have Felix stationed at the north entrance of the corridor, Ingrid at the south, and Sylvain by the door to the room we’ll be in.”

That last part certainly snapped Sylvain back to reality.

“I’m sorry, I’m going to be where now?” He made the mistake of looking Byleth in the eye. He forgot how to breathe. He must have completely missed what Byleth had to say because Ingrid punched him in the arm.

“Are you even listening Sylvain?” She sounded so disappointed in him, _as always_. Sylvain finally sucked in a breath and sat up straighter.

“Sorry I, uh, what were you saying Professor?”

“I was just saying that I’ll need you to be within ear shot in case it does get violent.”

_Ear shot…_

“And in case Dimitri tries to run, Ingrid and Felix will have the exits covered,” Byleth continued.

“And we are also keeping anyone from coming through there, right?” Ingrid asked.

“Yes, we want this to be as private an affair as we can.”

Felix scoffed, and thankfully gave Sylvain’s brain something else to focus on.

“So, we cover the exits while you tame the boar, easy enough.”

…

The night of the ‘mission’ held a soft chill in the air. Sylvain was leaning against the cool stone wall next to Felix. He was supposed to move into position once Dimitri was inside. It was almost time. Luckily, he and Felix were close enough that neither felt the need to break the silence with small talk. Sylvain enjoyed the momentary peace.

They heard the tired footsteps of their prince, a few knocks on the door, and then what they assumed to be him entering the dorm. Sylvain waited a few moments before moving into position. He remained tucked around the corner, but he could still hear most of what was happening in the room. He could hear Byleth’s voice, but wasn’t quite able to discern what was being said.

“Psst!”

Sylvain looked around the corner to see Ingrid peeking out from the far end of the hall.

“Have they started?” she mouthed to him. He lifted his head up in an attempt to listen better, but the talking had ceased and there wasn’t any sound coming from the room. He shrugged to which she dropped her face to her palm and shook her head.

Sylvain leaned back around his corner and let his head fall back against the stone. Despite his best efforts, his mind kept wondering how everything was going in there. He knew Byleth would remember to a tee what to do, but would Dimitri even be gentle with him?

_What if he hurts him?_

Sylvain’s cheeks were hot. The rustling of clothing caught his attention. _They were disrobing_. The image of Byleth, naked and under him flashed through his mind.

_Damn, dammit, why?_

The very thought of someone else getting to see that made him want to punch through the wall, and the fact that that very thing was happening next to him had him shaking.

“Oi, what the fuck are you doing Sylvain?” Felix whispered at him from down the hall. Sylvain looked back at him and brought a finger to his mouth and shushed him. But Felix was already silently approaching him.

“You’re supposed to be watching that exit,” Sylvain whispered back as he pointed to the other’s post.

“And you’re supposed to be guarding the door.”

“I am!”

“No, you look like you’re about to explode,” Felix said, still at a whisper, as he gave him a glance over.

“Guys, what the fuck?” Unbeknownst to them, Ingrid had also made her way down the hall. Before Sylvain could even make a noise, Felix answered her.

“Sylvain’s thinking with the wrong head.”

_OH MY GODDESS._

“I am _not_,” Sylvain hissed.

“Then why are you shaking?” Felix asked.

“I’m……cold.” Neither of them bought it. Ingrid rolled her eyes and turned to return to her post.

“Ugh, Sylvain just do your job.”

A few moments after she left, both Felix and Sylvain heard a moan from within the room. Sylvain’s eyes fluttered shut and his hands formed into fists.

“Oh, my goddess,” Felix said. “You’re _into this_?” Of course, his best friend would notice his flushed face and hardening dick in the dark like this.

Sylvain’s eyes opened and he glared at Felix, but another _<strike>beautiful</strike>_ lewd sound came from behind the door. The red head knew he probably looked horribly pathetic at this point: tears prickling in his eyes, growing erection, shaky breaths…he heard Felix scoff again. He figured he’d just turn and leave him to his own business, but a cool hand was suddenly over his mouth and another hand undoing his pants. Sylvain looked at him in shock, but Felix just shushed him as he took him in hand. He tried to speak, but the shorter man glared back at him with enough ferocity to shut him up.

And so there Sylvain was, pinned against the wall that had the man he was falling for on the other side in bed with someone else, getting jerked off by his best friend – _who wasn’t actually bad at it at all_. Sylvain closed his eyes and unashamedly felt more aroused at every noise he knew to be Byleth. He came startlingly quick, grabbing on to Felix for support. The latter simply let him finish and tucked him back into his pants, closed them, and rubbed his hand over Sylvain’s shirt to clean it off.

“Don’t say I never did anything for you, Gautier,” he said in a hushed even voice as he went back to his post.

It took Sylvain a few moments to regain his breath, and a few more to process what just happened. His head was significantly clearer now, though, and he was able to focus more on his duties.

_Wild._

Maybe his feelings were just byproducts of being really horny? Sylvain knew it could easily be possible. There weren’t exactly any available women at the monastery anymore. He shook his head and silently chuckled to himself – how pathetic it was to think himself in love when he really just needed to be touched.

…

That was **definitely not the case.**

When he saw Byleth that next day, attraction to the other man crashed over Sylvain like a wave. The surge of feelings for the other that stabbed into Sylvain’s heart almost knocked him flat on his ass.

**Notes for the Chapter:**

> Uh-oh, whatever is Sylvain going to do? ;)

**Author's Note:**

> There is so much more to come :)


End file.
